Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnly/openWorld annotations, it discloses credit costs, that empty result pages still cost, that invalid requests are free, that results span four collection types, and that items can repeat across pages so callers should deduplicate by ID. However, the cost information is internally inconsistent and clearly stitched from marketing boilerplate: '1 credit per page' alongside 'at least 10 Nexscope credits' and '1 credit per request' would leave an agent unsure what a call actually costs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The core guidance is well front-loaded, but the entire paragraph is duplicated verbatim and cluttered with scraped page artifacts ('YouTube Channel Search API View Pricing', '1 credit per request', 'Completed lookups cost at least 10 Nexscope credits'). Roughly half the text earns no place and actively introduces a pricing contradiction.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a three-parameter, no-output-schema search endpoint, an agent gets types of results, pagination, deduplication, and cost model — essentially everything needed to call it correctly. The only real gap is the conflicting credit figures, which should be resolved to a single number.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds genuine meaning beyond the schema: it clarifies the handle/query pair must stay constant across pagination and that passing the literal string null terminates with no charge, which the schema only hints at. It also tells the caller what the results can contain (videos, Shorts, lives, playlists in separate collections), which is not in the parameter docs.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The first sentence names a specific verb and resource ('Search within one YouTube channel') and explicitly rules out two plausible misinterpretations: global search and local filtering of the channel's latest videos. It also names the sibling that would otherwise be confusable (social_youtube_search) by contrast, so an agent can pick correctly without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It states when to use this tool, when not to (global search, latest-videos listing), the exact inputs (handle with or without @, keyword query), the pagination contract (reuse the same handle and query with continuationToken), and the termination condition (null token, with a literal null returning an uncharged terminal response). Unsupported filters are also enumerated, which prevents wasted calls.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.